Light emitting diodes (LEDs) are now the standard light source for a wide variety of illumination, warning, and signaling devices. LEDs include a semiconductor die (or chip) which emits light of a pre-determined wavelength (color) when energized by electrical power. The light emitting die is typically placed on a heat transmissive support, provided with conductive contacts to connect the die to an electrical circuit and may include a primary optic. The assembly of a light emitting die, heat transmissive support, electrical connections and primary optic (if present) may be referred to as an LED lamp. LED lamps in a variety of colors and light generating capacities are generally available. In some cases, several light emitting dies are placed on a common heat transmissive support. The light emitting dies may be of the same color or different colors. Some LED lamps provide primary color mixing necessary for color displays, with light emitting dies for each of the colors on a common support.
Light emitting dies emit light away from the heat transmissive support in a divergent pattern surrounding an optical axis passing through a center of the light emitting die. An LED lamp may include a primary optic that modifies the pattern of light emitted from the die or dies, but all LED lamps are “directional” light sources in that light is emitted in a direction away from the heat transmissive support. Lighting devices produce different light emission patterns suited to the purpose of the lighting device. Common light emission patterns include a collimated beam (spot), and evenly distributed (flood) patterns. Other emission patterns of partially collimated beams and shaped light emission patterns are also employed for particular purposes. Lighting devices include optical assemblies of lenses and/or reflectors to modify the light emission pattern of LED lamps to produce the desired light emission pattern. The optical assemblies are commonly constructed around a focal point or focal axis, and light emitted from the focal point or focal axis is handled accurately by the optical assembly. Light emitted at positions offset from the focal point or axis of the assembly is emitted from the assembly in an emission pattern that is different from the designed emission pattern. The ability of optical assemblies to generate a specific emission pattern is somewhat compromised by the fact that each light emitting die has an area, and light emitted from areas of the die spaced from the center of the die is offset from the optical focus or focal axis of the optical assembly. Large light emitting dies and large substrates with multiple dies may exaggerate this effect, which generally results in a blurred emission pattern.
Some lighting devices are configured to generate more than one light emission pattern. For example, a flashlight may be designed to emit both a focused beam (spot) and a diffuse (flood) light emission patterns. This is typically accomplished by moving the optical assembly relative to a single light source, which alters the pattern of light emitted. Other lighting devices may include multiple light sources, each with its own dedicated optical assembly and operate different light sources to generate specific patterns of light emission. Multiple optical assemblies can be costly to manufacture and may not be possible within the constraints applicable to a specific lighting device configuration.
There is a need in the art for lighting devices that can generate different light emission patterns utilizing the same stationary optical assembly with a single focus.